Warewash machine with soil detection

ABSTRACT

A conveyor-type warewash machine includes a conveyor mechanism for moving wares through a plurality of spray zones including at least one spray zone having spray nozzles for spraying recirculated liquid from a collection tank in the spray zone and a downstream final rinse zone with spray nozzles for spraying final rinse liquid. A sensor arrangement is located for monitoring condition of liquid of the collection tank. A control is operatively connected with the sensor arrangement and configured to vary flow rate of final rinse liquid sprayed from the final rinse nozzles based upon condition of liquid as indicated by the sensor arrangement.

CROSS-REFERENCES

This application is a continuation-in-part of U.S. application Ser. No.12/604,992, filed Oct. 23, 2009, the entirety of which is incorporatedherein by reference.

TECHNICAL FIELD

The present application relates generally to warewash machines of thecommercial type and, more particularly, to a commercial warewash machinewith water soiling level detection.

BACKGROUND

Modern commercial warewash equipment uses internally re-circulated waterduring the washing process and introduces clean hot water during therinsing and sanitization processes. The soil level of the internallyre-circulated water increases as dirty ware (e.g., dishes, cutlery, potsand pans) enters the machine over the course of an operational shift. Ifthe soil concentration reaches a critical level, the likelihood of soilre-deposition on to the ware increases.

Currently, the operator is primarily responsible to identify the issueof soil re-deposition and take corrective actions. Typical correctiveactions may include re-running ware, pausing the operation to partiallydrain the machine tank or tanks, and pausing the operation of themachine to clean the strainer/filters.

Ideally, the warewash machine would have the capability to monitor itsown soil level and take corrective actions (within a range of soillevels) without the interaction of the operator and reduction inproductivity.

A known approach to sense the level of soil in liquid using opticalmethods is the turbidity sensor. The use of turbidity sensors inresidential dishwashers is commonplace and the technology is readilyavailable. However, the migration of turbidity sensors to commercialwarewash equipment has been slow due to challenges unique to theirapplications. For example, commercial warewash equipment operates with amuch broader range of acceptable soil loads during the washing process.Existing turbidity sensors lack the dynamic range of operation for usein commercial warewash equipment. Additionally, existing turbiditycontrol logic does not adequately optimize the performance of acommercial dishwasher due to the different nature of the machine cycles.Moreover, commercial warewash equipment operates with higher washvolumes and flow rates resulting in a significantly more turbulentenvironment in the wash tank(s). The placement of turbidity sensors inthe prior art (e.g., in the tank or in line with wash waterrecirculation flow) does not allow for suitably accurate readings ofsoil level due to turbulence/bubbles, etc. in the wash water.

Accordingly, it would be desirable and advantageous to provide a soilsensing system that is more suited to the commercial warewash machineenvironment.

SUMMARY

In one aspect, a warewash machine includes a tank for holding liquid tobe sprayed on items in a spray chamber and a recirculation line fordelivering liquid from the tank to nozzles for spraying. A sensorarrangement is provided for monitoring (e.g., detecting) condition oftank liquid, the sensor arrangement including an light emitter and alight receiver. A control is provided for energizing the light emitterand monitoring (e.g., evaluating via hardware and/or software) output ofthe light receiver, wherein the control is configured to vary theenergization level of the light emitter during sensing to extend auseful range of measurement the sensor arrangement.

In another aspect, a warewash machine includes a tank for holding liquidto be sprayed on items in a spray chamber and a recirculation line fordelivering liquid from the tank to nozzles for spraying. A sensorarrangement is provided for monitoring condition of tank liquid, thesensor arrangement including an light emitter and a light receiver. Acontrol is provided for effecting energization of the light emitter andmonitoring output of the light receiver. The sensor arrangement islocated along a path that is one of a drain line of the tank or a linein parallel with the drain line, and the control is configured toimplement a liquid monitoring operation after liquid travel along thepath has stopped and a settling period has occurred.

In a further aspect, conveyor-type warewash machine includes a conveyormechanism for moving wares through a plurality of spray zones includingat least one spray zone having spray nozzles for spraying recirculatedliquid from a collection tank in the spray zone and a downstream finalrinse zone with spray nozzles for spraying final rinse liquid. A sensorarrangement is located for monitoring condition of liquid of thecollection tank. A control is operatively connected with the sensorarrangement and configured to vary flow rate of final rinse liquidsprayed from the final rinse nozzles based upon condition of liquid asindicated by the sensor arrangement.

In still a further aspect, a conveyor-type warewash machine includes aconveyor mechanism for moving wares through a plurality of spray zonesincluding at least a wash zone, a post wash zone downstream of the washzone, and a final rinse zone downstream of the post wash zone. The washzone includes spray nozzles for spraying recirculated wash liquid from acollection tank in the wash zone. The post wash zone includes spraynozzles for spraying recirculated post wash liquid from a collectiontank in the post wash zone. The final rinse zone includes spray nozzlesfor spraying final rinse liquid and having a pump or valve forcontrolling flow of final rinse liquid. The collection tank of the postwash zone is arranged such that some final rinse liquid sprayed from thespray nozzles of the final rinse zone is collected in the collectiontank of the post wash zone. A sensor arrangement is located formonitoring condition of post wash liquid of the collection tank of thepost wash zone. A control is operatively connected with the sensorarrangement and the pump or valve. The control is configured to controlthe pump or valve to increase flow rate of final rinse liquid sprayedfrom the final rinse nozzles upon the sensor arrangement indicating asoiled condition of the post wash liquid in order to reduce soil levelof post wash liquid of the collection tank of the post wash zone.

In another aspect, a method is provided for controlling soiling level ofwater in a conveyor-type warewasher having a conveyor mechanism formoving wares through a plurality of spray zones including at least awash zone, a post wash zone downstream of the wash zone, and a finalrinse zone downstream of the post wash zone, the wash zone includesspray nozzles for spraying recirculated wash liquid from a collectiontank in the wash zone, the post wash zone includes spray nozzles forspraying recirculated post wash liquid from a collection tank in thepost wash zone and the final rinse zone includes spray nozzles forspraying final rinse liquid, and the collection tank of the post washzone arranged such that some final rinse liquid sprayed from the spraynozzles of the final rinse zone is collected in the collection tank ofthe post wash zone, the method comprising: delivering final rinse liquidfrom spray nozzles at a first flow rate during washing; detecting asoiled condition of liquid of the post wash tank; and in response todetection of the soiled condition, at least temporarily delivering finalrinse liquid from the spray nozzles at a second flow rate duringwashing, the second flow rate higher than the first flow rate, so as toincrease collection of sprayed final rinse liquid in the collection tankof the post wash zone in order to reduce soil level of the post washliquid in the collection tank of the post wash zone.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of a warewash machineincorporating the soil level detection system;

FIG. 2 is a schematic diagram of the soil level detection sensorarrangement;

FIG. 3 is an alternative embodiment of a warewash machine incorporatingthe soil level detection system;

FIG. 4 is a timing diagram for an exemplary cycle of the machine of FIG.3; and

FIG. 5 is schematic diagram of an alternative conveyor-type machine.

DETAILED DESCRIPTION

Referring to FIG. 1, in one implementation, the soil detection system isimplemented in the context of a conveyor-type dishwasher 10 in whichitems to be washed are moved (e.g., right to left in FIG. 1 via aconveyance mechanism 12) through a housing 14 having multiple sprayzones 16, 18, 20 and 22 and, in some cases, a drying zone 24. Theconveyance mechanism 12 may be on suitable type, such as a continuousbelt-type with ware receiving slots or a reciprocating type configuredto move ware baskets containing ware.

By way of example, spray zone 16 may be a pre-wash zone, zone 18 may bea main wash zone, zone 20 may be a hot post-wash zone (also known as apower rinse zone) and zone 22 may be a final rinse zone. Additionalspray zones could be included, or a lesser number of spray zonesimplemented. As shown, the pre-wash zone 16 includes an associated watertank 26, pump 28 and line 30 forming a recirculation path in whichliquid is delivered from the tank 26 to nozzles 32 (e.g., located inupper and lower laterally extending spray arms) for spraying, and thesprayed liquid collects in the tank 26 for recirculation. Wash zone 18includes a similar tank 34, pump 36, line 38 and spray nozzles 40forming a recirculation flow path. Likewise, post-wash zone 20 includesa similar tank 42, pump 44, line 46 and nozzles 48 forming arecirculation flow path. Tank 42 is shown with an associated heatingelement 50 for heating the tank water, and one or both of tanks 34 and26 could include a heating element as well if desired.

The final rinse zone 22 includes an associated booster heater tank 52that receives water from a fresh water input source 54 through a valve56 or other feed structure (e.g., a pump). The booster tank 52 isconnected to deliver water via line 58 to nozzles 60 in the final rinsezone 22, and includes a heating element 62 for heating the rinse water.The booster tank could include an associated delime system.

One or more of the tanks 26, 34 and 42 may have an associated freshwater feed line 70, 72, 74 and related valve 76, 78, 80 to controldelivery of fresh water into the tank from a fresh water line 82 ifdesired.

The drying zone 24 includes a blower 84, which typically includes anassociated heater, for blowing hot air onto the wares after finalrinsing.

The final-rinse system may include an associated rinse aid supply 90 andpump 92 for delivering rinse aid to the booster 52, or alternatively tothe outfeed line of the booster, in a metered manner. The main wash zonemay include an associated detergent supply 96 and associated pump 98 fordelivering detergent to the tank 34, or alternatively directly into theline 38, in a metered manner. Other forms of detergent supply may beused, such as manual placement of a block/solid type detergent product.A controller 100 is provided for operating the various pumps, valves,conveyor and blower in accordance with one or more programmed cleaningsequences.

In order to address the limitations of the prior art as it applies tocommercial warewash machines both the dynamic range of the turbiditysensor should be increased and the position of the sensor be arranged toaccommodate the higher level of turbulence within commercial machines.In regard to sensor position, each of the tanks 26, 34, and 42 mayinclude an associated drain system (not shown in FIG. 1) enabling thetank to be drained, either partially or fully, in a controlled manner.By way of example, reference is made to FIG. 2 in which an exemplarytank drain system 102 is shown. The drain system includes a piping,tubing or hosing line 104 that connects to an outlet 106 of the tank andextends to a sensor assembly 108 that utilizes, in one example, a clearsquare tubing 110 that has an associated sensor module 112 mountedthereto. The sensor module 112 includes a light emitting element 114(e.g., one or more LEDs) on one side of the tube 110 and a lightreceiving element 116 (e.g., one or more phototransistors) on theopposite side of the tube 110. The lower end of the sensor assembly isconnected to drainage piping or tubing 118 that leads to a facilitydrain. A valve 120 may be used to control flow along the drain path, butin other embodiments a pumped drain system could be employed. While theillustrated sensor assembly 108 is shown in line with the primary drainpath of the tank, the sensor assembly could, alternatively, be connectedin parallel with the primary drain path (e.g., per dashed lineconfiguration 122). Interface connectors 124 and 126 (e.g., round tosquare transition couplers with associated clamps) may be provided forinterconnecting the sensor assembly in the drain path as shown. Thesensor elements include associated leads 128 and 130 that connect backto the controller 100 and power as needed. Additional electronic controlcircuitry may be associated with the sensor elements as needed.

An alternative sensor arrangement could include multipleLED-phototransistor pairs arranged or spaced apart vertically from eachother such that each pair is positioned for detection of soil level at adifferent height in the detection zone. For example, an implementationhaving three or more vertically spaced pairs could be beneficial inidentifying floating and settling particles. Specifically, assume thatthe turbidity of a water sample is initially determined and that overtime the turbidity indicated by the mid-height sensor pair is reflectsthat the water sample clears up. If the turbidity indicated by theLED-phototransistor pair below the mid-height pair increases, aconclusion can be drawn that particles are settling. The rate ofsettling may correspond to the size or density of such particles,enabling particle size to be used as a factor in machine control.Alternatively, if the turbidity indicated by the LED-phototransistorpair above the mid-height pair increases, a conclusion can be drawn thatparticles are floating.

Using the suggested sensor positioning, valve or pump cycles may be usedto collect a sample of the tank water sample at predetermined intervals.By way of example, the machine controller 100 generates a tank watersample signal and a sample of the tank water is gravity fed by openingthe valve 120 (or fed by a pump by operation of the pump) to the sensorassembly 108. A fresh tank sample may be obtained by momentarily openingthe valve or cycling a pump. The water sample is now within the sensorassembly. A sample settling time may be applied prior to triggering thesensor components for monitoring. It is advantageous to allow the sampleto settle for a short period of time to allow bubbles to escape andlarger particles to settle or float. The light emitting element isenergized and the output level of the light receiver monitored todetermine turbidity of the water sample. An evaluation can be made bythe controller 100 to determine whether any action is necessary basedupon the determined turbidity or soiling level. These actions mayrepeated as often as desired and in sequences as determined appropriatefor a given machine type.

Due to the range of soil encountered in a commercial warewash machine, atypical prior art sensor system would typically have adequate resolutionat very low levels of concentration and reach saturation well before thehighest acceptable levels of soil were reached for a commercial machine.If a single higher intensity turbidity sensor would be used, meaningfuldata would be lost at medium or low soil levels. In order to addressthis problem, varying the energization level of the light emittingelement is employed.

In one embodiment, a stepped light intensity technique is used. In oneimplementation, the stepped light intensity is achieved by applyingstepped energization levels for the light emitting element (e.g.,applying stepped voltage levels). In an alternative implementation, thestepped light intensity is achieved by using multiple light emittingelements (e.g., LEDs) and energizing less of the elements at lower stepsand more of the elements at higher steps. In this regard, a “lightemitter” may be made up of a single light element or multiple lightelements and, in the latter case, the energization of the light emittermay, in certain implementations, be varied by energizing differentnumbers of the light elements making up the light emitter. The followingis a description of an exemplary application/operation. Otherconfigurations may be utilized to produce similar results.

The light emitting element 114 illuminates. The light travels throughthe water sample to the light receiver 116. The more soiled the water,the less light transmitted to the light receiver 116. The light receiver116 (e.g., a phototransistor) outputs a voltage proportional to thelight received and, therefore, proportional to the water's soil level.As the soil level increases, the voltage increases. Alternatively, theelectronics could be set up so that as the soil level increases, thevoltage decreases. In either case, a proportional relationship is theresult.

A low light emitter intensity accurately allows the sensing of low soillevels but does not allow the accurate sensing of high soil levels. Athigh soil levels, the low light emitter intensity causes the sensor tosaturate (reaches maximum voltage level) making it impossible todetermine the higher soil levels. Conversely, a high light emitterintensity accurately allows the sensing of high soil levels but does notallow the accurate sensing of low soil levels. At lower soil levels, thehigh light emitter intensity causes the sensor to reach minimum voltagelevel (near 0 volts) thereby not being able to determine the lower soillevels. The solution is a sensor arrangement that puts out differentintensities of illumination, to accurately sense different soil levels.

In one implementation of the stepped approach, 3 illuminationintensities, low, medium, and high are used. Through experimentation,this has been adequate to sense required soil levels, though someapplications and soil levels may require a higher or lower number ofintensities.

The controller 100 may be configured to select which intensity to usefor the machine. Specifically, as each intensity level (low, medium,high) is illuminated, the voltage output level of the light receiver 116is captured and stored. These voltage output levels are compared and theintensity level that results in the light receiver voltage level closestto midrange of the light receiver is chosen for use. By way of example,and assuming use of a light receiver with a midrange voltage output oftwo volts, once soiled water has been delivered into the sensor assemblyand, if appropriate the settling time has passed, the controller 100effects energization of the light emitter 114 at the low intensity, andthe light receiver voltage output is 3.8 volts. The light emitter isnext energized at the medium intensity and the light receiver voltageoutput is 3.5 volts. The light emitter is next energized at the highintensity and the light receiver voltage output is 1.9 volts. Since thehigh intensity level results in the light receiver voltage output levelthat is closest to 2 volts, the controller 100 selects the highintensity level energization for use in machine control. A highintensity lookup table (e.g., stored in memory of the controller 100)may then be used determine any machine action necessary for the 1.9 voltoutput level of the light receiver 116.

In the above example, if the low intensity energization level resultedin the light receiver output that was closest to 2 volts, the controllerwould use that energization level for machine control and refer to a lowintensity lookup table to determine any machine action necessary.Likewise, if the medium intensity energization level resulted in thelight receiver output that was closest to 2 volts, the controller wouldused that energization level for machine control and refer to a mediumintensity lookup table to determine any machine action necessary. Thelook-up tables can be established in accordance with a calibrationsequence for the sensor assembly, which could be implemented prior tomounting of the sensor assembly on the machine, or afterward. In thelatter case, the calibration sequence could be incorporated into theprogram of the controller 100.

In this manner, machine control based upon water soiling level can bemore effectively maintained for low, medium and high soiling levels.

In another embodiment, varying of the light emitter energization levelmay be achieved by use of a ramped energization of the light emitter.For example, a complete and continuous range of light intensities from avery low level that can just produce a weak signal at the light receiverthrough very clear wash water to a very high intensity that can easilypenetrate very heavily soiled water may be implemented. A sensorarrangement that uses the described ramped light intensity may use alight emitter 114 (e.g., LED emitter) that is driven by a voltage rampthat causes light intensity levels of a range greater than needed forthe expected range of turbidity to allow for ageing and buildup on thesample tube. The light receiver 116 receives the light that has beenattenuated by the fluid in the sample tube 110 and produces a signalthat is compared to a predetermined reference value or set thresholdvalue (e.g. as determined by a calibration sequence). When the rampdriven light emitter 114 reaches an intensity that causes the lightreceiver output to equal the reference/threshold value, a comparisoncircuit switches and captures the analog value of the voltage ramp atthat instant. The value of the voltage ramp at that time is proportionalto the turbidity level of the fluid in the sample tube. The capturedturbidity value is then filtered and can be an input to the machinelogic control system (e.g., used to reference a look-up table todetermine responsive machine actions to be taken). The repetition rateof the turbidity sampling process can be changed for variousapplications. If the desire is to quantify particles suspended in theliquid sample then a high sampling rate on the order of several hundredsamples per second using the appropriate filtering may be used. If theinterest is only in the average turbidity, a slower sampling rate on theorder of several samples per minute with the corresponding filter wouldbe used.

Ageing and loss of clarity of the sample tube 110 is likely to occur inmost applications of the device and thus some compensation or correctionscheme may be implemented for continued proper measurements to be taken.One such scheme would be to periodically allow known clean liquid to bemeasured by the device and note the turbidity value which will begreater than when the sample tube was new. This measured valuerepresents the loss in light transmisitivity of the sample tube 110, andthis value can be subtracted from any subsequent reading on turbidliquids until the next calibration cycle is performed and a new offsetvalue is established.

The ramped implementation should be implemented such that the lightintensity range is large enough to cover the full range of expectedturbidity values and the possible loss of transmisitivity of the sampletube.

Both of the disclosed embodiments (i.e., stepped intensity and rampedintensity) will yield useful and valid data. The ramped approach willprovide a step-less, non overlapping range of values and may requirefewer components to manufacture. The stepped approach produces a rangeof values that may overlap and not be discrete, requiring moreintelligence in the appliance control system to properly interpret thedata and perform the appropriate action.

The stepped method may be advantageous if both average turbidity andparticle data is desired. Using the stepped method, once the properintensity step is chosen, the average turbidity level can be determinedand then the light emitter intensity level could be maintained insteadof switching to the next intensity in the sequence. During this extendedtime the variations in received signal from the light receiver 116(e.g., due to particle settling) could be processed to provide usefulinformation about the size and quantity of suspended particles in theliquid sample.

The stepped light intensity and ramp light intensity approaches allowfor soil samples to undergo a number of complete cycle sweeps within agiven time period. Useful information that characterizes the soil can begathered during the sweeps, specifically: (1) light receiver voltagelevel output (i.e., V(t)—discrete voltage values at points in timeindicate the turbidity level at that specific moment), useful for basicmeasurement and useful for setting action thresholds; (2) rate of changein light receiver voltage level output over time (i.e., dV/dt), which(i) can be calculated within a specific sample or from sample to sample,(ii) provides information related to the presence of particles in thesolution (e.g., the greater the rate of change indicates the greateramount of particles that are settling, which information is usefulbecause the presence of a significant amount of particles will increasethe likelihood of soil re-deposition) and (iii) provides informationrelated to the soil level trends; (3) variance in light receiver voltagelevel output (i.e., the variance of the light receiver voltage valueswithin a given period of time (applies to stepped approach), which (i)can be calculated over a given light emitter intensity and/or fromsample to sample and (ii) provides information related to the presenceof particles in the solution.

Referring now to FIG. 3, an alternative warewash machine embodiment isshown, which is of the box-type (also known as batch type or door typemachines). The machine 140 includes a housing 142 defining a washchamber 144 that is accessible by a door 146. The door may be pivotallymounted (e.g., in the case of an undercounter machine) or mounted forvertical, sliding movement (e.g., in the case of a hood-type machine).Wares are manually moved into the chamber 144 for cleaning, and manuallyremoved when the cleaning cycle has been completed. A sump tank 148 islocated below the chamber 144 and a pump 150 and line 152 are providedto deliver water from the sump to nozzles 154 of upper and lower sprayarms 156 (e.g., of the rotating type). A detergent supply 158 andassociated pump may be provided to deliver detergent to the sump 148 ina metered manner. Other forms of detergent supply may be used, such asmanual placement of a block/solid type detergent product. A boosterheater 162 receives water from a fresh water supply input 164 via avalve 166 or pump and has an output line 168 that delivers water to thenozzles 154 or, in the alternative, to a set of separate rinse arms withassociated nozzles (not shown). A rinse aid supply 170 and associatedpump 172 is provided to deliver rinse aid to the booster tank 162 in ametered manner. The sump 148 includes an associated drain outlet 174that leads to a sensor assembly 108 (shown in dashed line form as a box)which could be similar to that of FIG. 2. A drain valve 110 is providedto control draining, but a pumped drain line system could alternativelybe provided. A controller 180 is provided to operate the various valvesand pumps in accordance with one or more programmed cleaning cycles.

Machine actions based on determined turbidity/soil level will generallybe determined by the type and configuration of warewash machine with thegoal of reducing the potential for soil re-deposition. The basic typesof machines can be divided into two categories, the conveyor-type (e.g.,per FIG. 1) and the box-type (e.g., per FIG. 3).

In the case of the box-type machine, variables that can be controlledbased on the soil level in the sump tank 148 include, by way of example:(1) frequency and duration of wash (e.g., by controlling the duration ofoperation of pump 150), (2) drop down duration (i.e., the dwell timebetween the spraying of detergent laden wash liquid and the subsequentspraying of clean rinse liquid; e.g., by controlling when the boosterwater is delivered following cessation of pump 150 operation), (3)frequency and duration of draining of the sump tank 148 (e.g, viacontrol of valve 110), (4) rinse duration and/or rinse water volume(e.g., by controlling how long valve 166 is maintained open), (5) rinseaid dosing (e.g., by controlling operation of pump 172), (6) detergentdosing (e.g., by controlling operation of pump 160), (7) steam cycle (ifavailable), (8) drying duration (e.g., by controlling operation of ablower and/or heating element used during drying), (9) interruption ofthe wash with a partial drain followed by refill and continuation of thewash and (10) implementation of a partial or full drain after wash andrepetition of the wash cycle before rinse.

Referring to FIG. 4, in the case of the box-type machine an exemplarycycle Tc is delineated by a wash period W (e.g., during which detergentladen liquid is recirculated), a drop down period DD during whichrecirculation of wash liquid stops and the machine dwells to allowliquid to drop down off of the ware and a rinse period R during whichclean rinse liquid is sprayed on the wares. Two exemplary water sampletimes are shown at drain times D1 and D2. Sampling at D1 could primarilybe used to determine whether to modify wash duration, drop downduration, timing of drain time D2, volume drained at drain time D2,rinse duration, rinse aid dosing and detergent dosing. Sampling a D2could primarily be used to determine whether to modify drop downduration, introduction of a third drain time for sampling and itsassociated volume and rinse duration.

In the case of the conveyor-type machine variables that can becontrolled based on the soil level in the monitored tank or tanksinclude, by way of example: (1) dilution of pre-wash (e.g., bycontrolling valve 76), (2) dilution of main wash (e.g., by controllingvalve 78), (3) dilution of post wash (e.g., by controlling valve 80),(4) conveyor speed (e.g., by controlling a motor associated with theconveyor 12), (5) drain valves or drain pumps associated with the tanks,(6) final rinse flow rate (e.g., by controlling valve 56 or a pumpassociated with the rinse line), (7) wash flow rate (e.g., bycontrolling operation of pump 36), (8) frequency and duration of tankdrains, (9) rinse aid dosing (e.g., by controlling operation of pump 92)and (10) detergent dosing (e.g., by controlling operation of pump 98.

On occasion, it may be desirable to check the integrity of the soilsensor assembly 108. A method is to inject clean water into the sensormay be provided and the sensor arrangement operated. If the lightreceiver voltage levels are not within a set tolerance and/or if thesoil sensor assembly operation stops, an error message is given (e.g.,via the controller 100 to energize a visual or audible annunciator). Anerror offset may allow for continued operation.

Referring now to FIG. 5, in another embodiment, a conveyor-type warewashmachine includes a conveyor mechanism 12 for moving wares through aplurality of spray zones 16, 18, 20 and 22 and a drying zone 24. Theconveying direction is right to left in FIG. 5. Each spray zone hasrespective spray nozzles 32, 40, 48 and 60 for spraying pre wash liquid(in the case of pre wash zone 16), main wash liquid (in the case of mainwash zone 18), post wash liquid (in the case of post wash zone 20) andfinal rinse liquid (in the case of final rinse zone 22). In the case ofzones 16, 18 and 20 the sprayed liquid is recirculated from respectivecollection tanks 26, 34 and 42. A sensor arrangement 108 or 108′ isprovided for monitoring condition of liquid of post wash collection tank42. In the case of sensor arrangement 108, the arrangement is locatedalong a bypass flow path line 140 that runs from the post washcollection tank 42 to the upstream pre wash zone 16 that is used toselectively deliver post wash liquid to the upstream zone under controlof a pump 152 (e.g., via opening of valve 150). Alternative sensorarrangement 108′ is located along a drain path 104 of the post washcollection tank 42. In another variation the sensor arrangement could bewithin the tank 42 itself.

As shown by arrow 156, the post wash collection tank collects some finalrinse liquid that is sprayed from the final rinse nozzles 60. A reverseoverflow system delivers excessive water in tank 42 upstream to tank 34,and overflow from tank 34 is delivered to upstream to tank 26.

A control 100 is operatively connected with the sensor arrangement 108,108′ and is configured to vary flow rate of final rinse liquid sprayedfrom the final rinse nozzles 60 based upon condition of liquid asindicated by the sensor arrangement 108, 108′. In this regard, thecontrol 100 is connected to control operation of a pump 154 to controlthe final rinse liquid flow rate, but alternatively could be connectedto control another flow control device such as a valve in the finalrinse liquid feed path. The control 100 is preferably configured toincrease flow rate of final rinse liquid sprayed from the final rinsenozzles 60 in response to the sensor arrangement 108, 108′ indicating asoiled condition of the post wash liquid of tank 42 in order to reducesoil level of post wash liquid of the collection tank of the post washzone. Specifically, the increased flow rate of final rinse liquidresults in collection of more sprayed final rinse liquid in the tank 42.Because the sprayed final rinse liquid is relatively clean as comparedto the liquid of the tank 42, this increased collection more quicklyreduces the soiling level in the tank 42.

The embodiment of FIG. 5 provides a method of controlling soiling levelof water in a conveyor-type warewasher of the type having a conveyormechanism 12 for moving wares through a plurality of spray zonesincluding at least a wash zone 16, 18, a post wash zone 20 downstream ofthe wash zone, and a final rinse zone 22 downstream of the post washzone, where the wash zone includes spray nozzles 32, 40 for sprayingrecirculated wash liquid from a collection tank 26, 34 in the wash zone,the post wash zone includes spray nozzles 48 for spraying recirculatedpost wash liquid from a collection tank 42 in the post wash zone and thefinal rinse zone 22 includes spray nozzles 60 for spraying final rinseliquid, and the collection tank 42 of the post wash zone is arrangedsuch that some final rinse liquid sprayed from the spray nozzles of thefinal rinse zone is collected in the collection tank of the post washzone. The method involves: delivering final rinse liquid from spraynozzles at a first flow rate during washing; detecting a soiledcondition of liquid of the post wash tank; and in response to detectionof the soiled condition, at least temporarily delivering final rinseliquid from the spray nozzles at a second flow rate during washing, thesecond flow rate higher than the first flow rate, so as to increasecollection of sprayed final rinse liquid in the collection tank of thepost wash zone in order to reduce soil level of the post wash liquid inthe collection tank of the post wash zone. The detecting step mayinvolve utilizing a sensor arrangement located in a flow path line thatextends from the post wash tank to the wash zone for selectivelydelivering post wash liquid from the post wash tank to the wash zoneunder control of a pump, or may involve utilizing a sensor arrangementlocated in the collection tank of the post wash zone or in a drain lineassociated with the collection tank of the post wash zone.

Although the invention has been described and illustrated in detail itis to be clearly understood that the same is intended by way ofillustration and example only and is not intended to be taken by way oflimitation. It is recognized that numerous other variations exist,including both narrowing and broadening variations of the appendedclaims.

1. A conveyor-type warewash machine, comprising: a conveyor mechanismfor moving wares through a plurality of spray zones including at leastone spray zone having spray nozzles for spraying recirculated liquidfrom a collection tank in the spray zone and a downstream final rinsezone with spray nozzles for spraying final rinse liquid; a sensorarrangement for monitoring condition of liquid of the collection tank;and a control operatively connected with the sensor arrangement andconfigured to vary flow rate of final rinse liquid sprayed from thefinal rinse nozzles based upon condition of liquid as indicated by thesensor arrangement.
 2. The conveyor-type warewash machine of claim 1,wherein the machine includes: a wash zone and a post wash zonedownstream of the wash zone, the final rinse zone downstream of the postwash zone, wherein the spray zone is one of the wash zone or the postwash zone, the wash zone includes spray nozzles for sprayingrecirculated wash liquid from a collection tank in the wash zone, thepost wash zone includes spray nozzles for spraying recirculated postwash liquid from a collection tank in the post wash zone.
 3. Theconveyor-type machine of claim 1 wherein the machine is arranged suchthat some final rinse liquid sprayed from the spray nozzles of the finalrinse zone is collected in the collection tank of the post wash zone,the sensor arrangement is located for monitoring condition of post washliquid of the collection tank of the post wash zone, and the control isconfigured to increase flow rate of final rinse liquid sprayed from thefinal rinse nozzles in response to the sensor arrangement indicating asoiled condition of the post wash liquid in order to reduce soil levelof post wash liquid of the collection tank of the post wash zone.
 4. Theconveyor-type machine of claim 1 wherein the control is operativelyconnected with a valve or pump that is connected in line to vary flowrate to the spray nozzles of the final rinse zone.
 5. The conveyor-typemachine of claim 1, including: a bypass flow path line extending fromthe collection tank of the post wash zone to an upstream zone of themachine for selectively delivering post wash liquid to the upstream zoneunder control of a pump; wherein the sensor arrangement is located alongthe bypass flow path line.
 6. The conveyor-type machine of claim 1wherein the sensor arrangement is located in the collection tank.
 7. Aconveyor-type warewash machine, comprising: a conveyor mechanism formoving wares through a plurality of spray zones including at least awash zone, a post wash zone downstream of the wash zone, and a finalrinse zone downstream of the post wash zone, wherein the wash zoneincludes spray nozzles for spraying recirculated wash liquid from acollection tank in the wash zone, the post wash zone includes spraynozzles for spraying recirculated post wash liquid from a collectiontank in the post wash zone and the final rinse zone includes spraynozzles for spraying final rinse liquid and having a pump or valve forcontrolling flow of final rinse liquid, the collection tank of the postwash zone arranged such that some final rinse liquid sprayed from thespray nozzles of the final rinse zone is collected in the collectiontank of the post wash zone; a sensor arrangement for monitoringcondition of post wash liquid of the collection tank of the post washzone; and a control operatively connected with the sensor arrangementand the pump or valve, the control configured to control the pump orvalve to increase flow rate of final rinse liquid sprayed from the finalrinse nozzles upon the sensor arrangement indicating a soiled conditionof the post wash liquid in order to reduce soil level of post washliquid of the collection tank of the post wash zone.
 8. Theconveyor-type machine of claim 7, including: a flow path line extendingfrom the collection tank of the post wash zone to the wash zone forselectively delivering post wash liquid from the post wash tank to thewash zone under control of a pump; wherein the sensor arrangement islocated along the flow path line.
 9. The conveyor-type machine of claim8 wherein the wash zone is one of a pre-wash zone or a main wash zone.10. The conveyor-type machine of claim 7 wherein the sensor arrangementis located in the collection tank of the post wash zone or in a drainline associated with the collection tank of the post wash zone.
 11. Amethod of controlling soiling level of water in a conveyor-typewarewasher having a conveyor mechanism for moving wares through aplurality of spray zones including at least a wash zone, a post washzone downstream of the wash zone, and a final rinse zone downstream ofthe post wash zone, the wash zone includes spray nozzles for sprayingrecirculated wash liquid from a collection tank in the wash zone, thepost wash zone includes spray nozzles for spraying recirculated postwash liquid from a collection tank in the post wash zone and the finalrinse zone includes spray nozzles for spraying final rinse liquid, andthe collection tank of the post wash zone arranged such that some finalrinse liquid sprayed from the spray nozzles of the final rinse zone iscollected in the collection tank of the post wash zone, the methodcomprising: delivering final rinse liquid from spray nozzles at a firstflow rate during washing; detecting a soiled condition of liquid of thepost wash tank; and in response to detection of the soiled condition, atleast temporarily delivering final rinse liquid from the spray nozzlesat a second flow rate during washing, the second flow rate higher thanthe first flow rate, so as to increase collection of sprayed final rinseliquid in the collection tank of the post wash zone in order to reducesoil level of the post wash liquid in the collection tank of the postwash zone.
 12. The method of claim 11, wherein the detecting stepinvolves utilizing a sensor arrangement located in a flow path line thatextends from the post wash tank to the wash zone for selectivelydelivering post wash liquid from the post wash tank to the wash zoneunder control of a pump.
 13. The method of claim 11, wherein thedetecting step involves utilizing a sensor arrangement located in thecollection tank of the post wash zone or in a drain line associated withthe collection tank of the post wash zone.